Start Microsoft Word or any other Office app and look at the splash screen

When you start any Microsoft Office app, before it loads, it quickly displays a Startingscreen. This screen is shown for a second or two, and it tells you the name of the app that you are using and the version. Here is the starting screen for Word, in Microsoft Office 2019.

Starting Word in Office 2019

If you use the Microsoft Office 365 subscription, it says Office 365, like in the screenshot below. This subscription ensures that you get access to the latest version of Office developed by Microsoft.

Starting Word in Office 365

Below you can see a sample of the starting screen of Word, in Microsoft Office 2010.

Starting Word in Office 2010

Also, another from the old Microsoft Office 2003.

Starting Word in Office 2003

Unfortunately, this method does not tell whether you use a 64-bit or 32-bit version of Microsoft Office, nor does it share the exact product version and build number.